After four to six weeks on a low-carbohydrate, high-fat diet, trained athletes maintain the same endurance performance during high-intensity exercise tests, including time trials and prolonged...
Mechanism
Synthesis from 1 study
After adapting to a low-carb, high-fat diet, muscles learn to burn fat so efficiently that they don't need stored sugar to power intense exercise. When you exercise for a long time, your blood sugar drops, and your brain stops you from continuing — but adding a little sugar during exercise fixes...
Most probable mechanism
When the body adapts to a low-carb, high-fat diet, it becomes much better at burning fat for energy, even during intense exercise. This allows muscles to get almost all their fuel from fat instead of stored sugar, so they don't need large amounts of glycogen to keep going. Fat burning provides enough energy to power high-intensity efforts up to 85% of maximum oxygen use. If blood sugar drops too low during long exercise, the brain signals fatigue, but adding a small amount of sugar during exercise prevents this drop and restores performance — proving the brain, not muscle sugar stores, controls when you stop.
Chronic carbohydrate restriction lowers insulin levels and increases circulating free fatty acids and ketone bodies, triggering metabolic adaptation in skeletal muscle.
Skeletal muscle upregulates fatty acid transport proteins and mitochondrial enzymes that enhance the capacity to oxidize fatty acids.
Fat oxidation rates increase to levels sufficient to supply over 90% of energy demands during high-intensity exercise up to 85% VO2max.
Muscle glycogen stores are reduced but are not required for ATP production during submaximal and high-intensity endurance exercise.
During prolonged exercise, hepatic glycogen depletion reduces endogenous glucose production, causing blood glucose to decline.
When blood glucose falls below a critical threshold, central nervous system fatigue mechanisms are activated, reducing motor output and terminating exercise.
Ingestion of 10 g/h of carbohydrate maintains blood glucose concentration, preventing central fatigue and restoring endurance capacity regardless of muscle glycogen levels.
Evidence from Studies
Supporting (1)
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Does a low-carbohydrate diet impede endurance sports performance? No
Contradicting (0)
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